1. Field of the Invention
The present invention relates to a device for sizing and/or finishing the external surface of a workpiece having a circular sectional contour, such as, a cylinder, and more particularly the invention relates to a burnishing device for continuously rolling the external surface of such workpiece of a relatively long type.
2. Description of the Prior Art
Methods heretofore known for producing a relatively high degree of surface finish on the external surface of a round workpiece, such as, a column or cylinder include polishing, lapping, superfinish cutting and burnishing. Of these methods, the burnishing is used effectively since this method is capable of simultaneously attaining an increased surface hardness, surface finish close to mirror finish and improved dimensional accuracy.
Burnishing tools of various shapes are provided to meet the needs for the treatment of work surfaces of various forms. Presently, the tools of many different shapes are in use for the working of such surfaces as bore inner surfaces, cylinder end faces, cone outer surfaces, cone inner surfaces, column outer surfaces, flat surfaces and spherical surfaces. These conventionally used burnishing devices are generally of the type in which the tool is mechanically pressed against or moved along the surface of a workpiece to apply the tool to the desired work surface. In other words, the tool is driven in both rotary and propelling motions relative to the workpiece so as to perform the burnishing operation over the desired range while changing its working position. The fact of requiring the two driving operations, rotating and propelling movements, gives rise to the disadvantage of complicating the processing operation. In particular, when processing the external surface of a long columnar or cylindrical workpiece to which the invention is directed, the propelling movement is required over the whole length of the long workpiece thus making the device bulky.
Devices heretofore proposed to overcome the foregoing deficiencies include for example a workpiece self-advancing type device disclosed in U.S. Pat. No. 3,626,560. The device stated in this U.S. patent is constructed so that a hollow head externally enclosing a plurality of truncated conical rollers arranged parallel to each other in a cage-like form is driven in rotation and therefore the rotational speed during the rotation of the head must be considerably high in order to rotate the rollers at a given rotational speed. In order that the degrees of the quality and finish of a workpiece may be controlled at the desired values, it is the usual practice to variably control the rotational speed of the tool and therefore in the device of the previously mentioned U.S. patent the high rotational speed must be variably controlled, thus causing the control to tend to become difficult and complicated. Also, in order to drive the head in rotation, the surrounding structure of the head is complicated and it is essential to include the built-in springs in the mechanism for adjusting the finished outer diameter thus causing complication of the construction and the occurrence of faults or troubles.